1. Technical Field
The present invention relates to a wiring member used in a liquid ejecting head such as an ink jet printing head and a liquid ejecting head having the same, and particularly, to a liquid ejecting head wiring member having wiring terminal rows formed by arranging wiring terminals respectively corresponding to pressure generating elements of a liquid ejecting head and a liquid ejecting head having the same.
2. Related Art
As one type of liquid ejecting head that ejects a liquid droplet from a nozzle by causing a variation in pressure of a liquid inside a pressure chamber, a liquid ejecting head configured to eject a liquid droplet by deforming a piezoelectric element (which is one kind of pressure generating element) bonded to a vibration plate is known. In this liquid ejecting head, the volume of the pressure chamber changes by driving the piezoelectric element in accordance with the application of the driving voltage (the driving pulse), the pressure of the liquid stored inside the pressure chamber changes, and then the liquid droplet is ejected from the nozzle by using a variation in the pressure.
A film-shaped wiring member (hereinafter, referred to as a flexible cable) such as a COF (Chip On Film) or a TCP (Tape Carrier Package) having an IC installed thereon to drive the piezoelectric element is electrically connected to the piezoelectric element, and a driving voltage is supplied via the flexible cable (for example, refer to JP-A-2005-254616). The piezoelectric element includes a lower electrode film, a piezoelectric body layer, and an upper electrode film. Generally, one electrode (for example, the lower electrode film) is used as a common element electrode commonly used with a plurality of piezoelectric elements, and the other electrode (for example, the upper electrode film) is used as an individual element electrode individually patterned for each of the piezoelectric elements. The piezoelectric body layer interposed between the common element electrode and the individual element electrode is a piezoelectric body activating portion that undergoes piezoelectric strain in accordance with the application of a driving voltage between both electrodes.
FIG. 7 is a schematic diagram illustrating a layout of an element electrode wiring portion (a lead electrode portion) extending from an element electrode and an element electrode of a piezoelectric element of an actuator unit 69 (refer to FIG. 8) of an existing printing head. Further, in the same drawing, the dark hatching portion indicates an individual element electrode and an individual element electrode wiring portion electrically connected thereto, and the light hatching portion indicates a common element electrode and a common element electrode wiring portion electrically connected thereto. Furthermore, in the same drawing, the vertical direction is the nozzle arrangement direction (the arrangement direction of the piezoelectric elements). A pressure chamber and a piezoelectric element are formed so as to correspond to each of the nozzles, and in the same drawing, only two rows of nozzles are shown.
In the configuration shown in the drawing, common element electrodes 70 commonly used with the piezoelectric elements are continuously formed on an elastic film (not shown) defining a part of the pressure chamber in the nozzle row direction, and an piezoelectric body layer (not shown) and an individual element electrode 71 are sequentially laminated thereon so as to be patterned for each of the piezoelectric elements. An individual element electrode terminal 72 (which is one kind of individual element electrode wiring portion) is formed between the adjacent nozzle rows while being electrically connected to the electrode 71 so as to correspond to each of the individual element electrodes 71. An individual element electrode terminal 72a corresponding to one nozzle row (on the left side of the drawing) and an individual element electrode terminal 72b corresponding to the other nozzle row (on the right side of the drawing) are arranged in a row shape so as to deviate from each other in the nozzle row direction. The individual element electrode terminal 72 is a portion that is electrically connected to a one-end-side individual electrode wiring terminal 77 (refer to FIG. 8) of a flexible cable 68.
Further, a common element electrode portion 73 (which is one kind of common element electrode wiring portions) is formed so as to surround the common element electrode 70, the individual element electrode 71, and the individual element electrode terminal 72. The common element electrode portion 73 is formed in a frame shape including a common vertical electrode portion 73a which extends in the nozzle row direction on the outside of the nozzle row direction (the opposite side of the individual element terminal formation side) of each of the nozzle rows, and a common transverse electrode portion 73b which extends in a direction perpendicular to the nozzle row direction on both sides of the nozzle row direction. The common element electrode portion 73 is electrically connected to each of the common element electrodes 70 via a branch electrode portion 74. In addition, a portion located on both sides in the arrangement direction of the individual element electrode terminal 72, that is, a portion surrounded by the dashed circle in the drawing in the common element electrode portion 73 is a common element electrode terminal 75 that is bonded to the common electrode wiring terminal 78 of the flexible cable.
As shown in FIG. 8, the flexible cable 68 has a configuration in which a control IC 76 is mounted on a surface of a base film such as polyimide so as to control the driving voltage applied to the piezoelectric element, a wiring pattern (not shown) of the individual electrode wiring or the common electrode wiring is formed thereon, and then the control IC 76 or the wiring pattern other than the wiring terminal (the individual electrode wiring terminal 77 and the common electrode wiring terminal 78) is covered by a resist. Further, a plurality of the one-end-side individual electrode wiring terminals 77 is formed at one end portion of the flexible cable so as to respectively correspond to the individual element electrode terminals 72 of the actuator unit. Furthermore, the one-end-side common electrode wiring terminal 78 is formed on the outside of the arrangement direction of the one-end-side individual electrode wiring terminal group at the one end portion so as to correspond to the common element electrode terminal 75 of the actuator unit. In addition, one end portion of the flexible cable is bent at a substantially right angle toward the opposite side of the surface provided with the wiring pattern and the like between the wiring terminal formation area and the wiring pattern formation area. Each of the wiring terminals 77 and 78 is subjected to solder plating in advance, the wiring terminals 77 and 78 are soldered to the corresponding element terminals 71 and 75 on the side of the actuator unit so as to be electrically connected thereto, and then the flexible cable 68 is attached to the actuator unit 69.
However, in existing printing heads, as described above, the common electrode wiring, the individual electrode wiring, the wiring terminals, and the driving control IC are provided on one flexible cable, and the proportion of the area provided with the common electrode wiring becomes smaller than that of the area of the driving control IC or the individual electrode wiring due to the limitation in the installation space. Then, when the wiring space involved with the common electrode is narrow due to the common element electrode wiring portion of the actuator unit, a decrease in the voltage occurs within the plane of the electrode in accordance with the resistance of the electrode, and the driving voltage applied to the piezoelectric element becomes irregular. Accordingly, there is concern that the weight or the flight speed of the ink ejected from the nozzle may become irregular. Particularly, the possibility of causing the above-described inconvenience increases as the number of nozzles simultaneously ejecting the ink increases. In order to suppress this inconvenience, existing printing heads require a larger area for the common element electrode wiring portion in the actuator unit, and a decrease in the size of the printing head by the amount of the increased area is not easily realized.